When an existing transmission device capable of transmitting E1 signals is to be additionally provided with a LAN (Local Area Network) packet transmitting function, it is necessary to change the radio frame structure or to newly introduce a device capable of transmitting LAN packets. As a result, an enormous cost is required for adding a function of transmitting LAN packets to the existing transmission device capable of transmitting E1 signals. The term “E1 signal” refers to an E1 interface signal standardized in ITU-T G.704. The term “LAN packet” refers to an interface signal standardized in IEEE802.3.
Thus, there is a demand for development of a method capable of facilitating the addition of a LAN packet transmitting function to existing transmission devices capable of transmitting E1 signals.
There exists literature disclosing a technique to transmit LAN packets using a plurality of transmission lines, regardless of E1 signals (see Patent Document 1, for example).
According to the technique described in Patent Document 1, stream data is divided in predetermined units and assigned to a plurality of transmission lines. On the other hand, information relating to these transmission lines is acquired as a transmission line list. The divided stream data and the transmission line list are sent onto the plurality of transmission lines. The divided stream data is reconstructed, on a reception side, based on the transmission line list acquired through one of the transmission lines. Referring to FIG. 6, the aforementioned processing operation disclosed in Patent Document 1 will be described.
A device shown in FIG. 6 is a device for providing information to an arbitrary device (not shown) connected to an ISDN (Integrated Services Digital Network) 64. This device includes a personal computer 50. The personal computer 50 is connected to Internet 11 through a LAN 10. The personal computer 50 is also connected to three subscriber lines 63(1), 63(2), 63(3) via terminal adapters (TAs) 61 and network terminations (NTs) 62. The three subscriber lines 63(1), 63(2), 63(3) are connected to the ISDN 64. A LAN interface 51 receives stream data from the Internet 11 through the LAN 10. A packet acquisition unit 52 extracts packet data from the stream data in units of packets. A packet sorting unit 53 sorts and assigns the packet data extracted in units of packets to the three subscriber lines 63(1), 63(2), 63(3) as transmission destinations. A transmission line list holding unit 54 holds ISDN numbers (line numbers) corresponding to the subscriber lines 63(1), 63(2), 63(3) as a transmission line list, and outputs the transmission line list to transmission line list adding units 55(1), 55(2), 55(3). The transmission line list adding units 55(1), 55(2), 55(3) add the transmission line list acquired from the transmission line list holding unit 54 to the packet data assigned by the packet sorting unit 53, and transmit the packet data to the subscriber lines 63(1), 63(2), 63(3) through interfaces 56(1), 56(2), 56(3), TAs 61(1), 61(2), 61(3), and NTs 62(1), 62(2), 62(3), respectively. In this manner, the technique described in Patent Document 1 makes it possible to divide stream data into pieces of packet data and transmit them using the plurality of subscriber lines 63(1), 63(2), 63(3).
According to the method of Patent Document 1, however, the transmission line list must always be added to the packet data sent onto each transmission line (subscriber line). Moreover, the information amount of the transmission line list is increased as the number of transmission lines to send the packet data is increased. Therefore, according to the method of Patent Document 1, the proportion occupied by packet data to be transmitted becomes smaller. As a result, according to the method of Patent Document 1, the actual throughput becomes lower than the transmission capacity of the transmission lines as the number of transmission lines to send the packet data is increased. This means that efficient transmission of packet data cannot be realized by the method of Patent Document 1.
Further, there exists literature disclosing a technique in which ATM
(Asynchronous Transfer Mode) cells are mapped to E1 frame time slots, and the ATM cells are sequentially mapped and transmitted at one-multiframe cycle (see Patent Document 2, for example).
There also exists literature disclosing a technique in which signals are distributed to and transmitted through a plurality of systems having varying transmission delay time, and the distributed and transmitted signals can then be synthesized to restore the original signal (see Patent Document 3, for example).
Further, there exists literature disclosing a technique as described below (see Patent Document 4, for example).
One data frame is divided according to respective system transmission speeds to produce a plurality of data packets having an equal packet length which is equal to or less than a maximum data size. The plurality of data packets thus produced are transmitted in parallel by a plurality of radio channels, or by a single radio channel and space division multiplexing, or by a plurality of radio channels and space division multiplexing.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-299704
Patent Document 2: Japanese Laid-Open Patent Publication No. H10-173658
Patent Document 3: Japanese Laid-Open Patent Publication No. 2002-335297
Patent Document 4: WO2004/114609